Rotary compressors are used in a variety of applications for compressing gases. As an example, with reference to FIG. 1, in turbocharger technology a rotating compressor wheel 11 within a compressor housing 13 sucks air through an intake port 15, compresses it in an impeller passage 17, and diffuses it into a volute 19. The compressed air is supplied to an intake manifold of an internal combustion engine. The operating range of a compressor extends from a surge condition (wherein the airflow is “surging”), occurring at low airflow rates, to a choke condition (wherein the airflow is “choking”) experienced at high airflow rates. Surging airflow occurs when a compressor operates at a relatively low flow rate with respect to the compressor pressure ratio, and the resulting flow of air throughout the compressor becomes unstable. “Choking” occurs when a compressor tries to operate at a high flow rate that reaches the mass flow rate available through the limited area of an intake end of the compressor wheel (known as the inducer) through which air arrives at the compressor wheel.
In order to improve the operating flow range, some compressors include one or more bypass ports 21 (such as in the form of an annular opening) on a compressor housing inner wall 23 (also referred to as a shroud) of the impeller passage 17 surrounding the compressor wheel 11. This “ported shroud” forms a bypass passageway 25 that extends between the bypass port(s) and a substantially annular opening 27 into the intake port 15 that feeds air in to the impeller passage. The ported shroud thus creates a second passage connecting the intake port to the impeller passage, wherein this second passage does not extend through the inducer.
The ported shroud typically improves the surge characteristics of a compressor by rerouting some air passing through the impeller passage back to the intake port during low-airflow operation, thereby extending the range over which the compressor can operate without experiencing a surge condition. The ported shroud may improve the choke characteristics of a compressor by providing an additional flow path into the impeller passage that does not extend through the inducer during high-airflow operation. This extends the range over which the compressor can operate without experiencing a choke condition.
When the bypass port 21 is in the form of an annular opening, it is necessary to have support structure to hold an upstream portion 31 of the compressor, which forms the portion of the compressor housing inner wall that is upstream from the bypass port, with respect to a downstream portion 33 of the compressor, which forms the portion of the compressor housing inner wall that is downstream from the bypass port. This support structure is typically a plurality of radial ribs 35 extend axially through the bypass passageway 25.
Airflow received through the bypass port 21 from the impeller passage 17, i.e., bypass air, typically has a flow vector including both a substantial axial component (i.e., a component of flow direction through the bypass passageway 25 and parallel to the compressor wheel axis of rotation) and a substantial circumferential component (i.e., a component of flow direction tangent to the circumference of the bypass passageway at that location). The circumferential component may be useful in reducing the angle of incidence between air passing through the bypass passageway and external air initially entering the compressor housing. Radial ribs that extend axially through the bypass passageway guide the airflow in an axial direction, obstruct the circumferential component of the airflow, and therefore reduce the circumferential component of the flow vector.
Accordingly, there has existed a need for an apparatus and related methods to extend the flow range of a compressor without reducing the circumferential component of the bypass air. Moreover, it is preferable that such apparatus are cost and weight efficient. Preferred embodiments of the present invention satisfy these and other needs, and provide further related advantages.